Torque indicator for fixed screw leads

ABSTRACT

A body-implantable lead (10) for use in cardiac pacing having a proximal end and a distal end, the proximal end connected to a medical device, an active fixation device such as a helix electrode (330) having a distal end and a proximal end, the tissue securing means extending from the lead body distal end, an electrical conductor (15) extending between the proximal and distal ends of the lead, and a longitudinally extending radiopaque marker (35 or 335) affixed to the lead body (10) proximal to the tissue securing means, the radiopaque marker (35 or 335) showing rotational movement or distortion of the radiopaque marker (35 or 335) under fluoroscopy.

FIELD OF THE INVENTION

The present invention relates to a lead bearing an electrode forelectrically connecting an organ inside a living animal body to anelectrical device and more particularly to cardiac pacing leads.

BACKGROUND OF THE INVENTION

There are generally two types of body-implantable leads used withcardiac pacemakers, myocardial and endocardial. Myocardial leadspresently require surgery to expose the myocardial tissue to which theelectrode is affixed.

Endocardial leads have an electrode or electrodes located at the distalend, are inserted in and guided through a body vessel such as a veininto the heart where the electrodes contact, and in some cases, aresecured to the heart through the endothelial tissue lining the heartinterior. Endocardial leads are divided into active and passive fixationleads. Passive fixation leads are nonpenetrating leads. Tines are anexample of passive fixation leads. Active fixation leads are penetratingleads. Applicant's fixed screw lead is an example of an active fixationlead.

An important feature of an endocardial lead is that of having a means ofsecuring the electrode to the heart without dislodgment. Active fixationleads reduce dislodgments. A disadvantage of prior art leads is that itis difficult to know when the lead has been successfully embedded in thecardiac tissue. With a fixed screw lead it is difficult to judge howmany turns are necessary to embed or remove the helix without turningthe lead too many times thereby causing undue trauma to the tissue. Withsuch leads, the physician must tactually determine the number ofrotations necessary to achieve lead fixation.

Endocardial screw-in type leads are well known in the art as forexample, U.S. Pat. No. 4,146,036 to Dutcher et al which discloses aunipolar fixed screw lead. With such leads, the physician tactuallydetermines the number of rotations necessary to achieve lead fixation.

U.S. Pat. No. 4,570,642 to Kane et al discloses an endocardial,unipolar, extendable screw-in lead. With such leads, the physicianobserves helix extension under fluoroscopy during lead fixation.

U.S. Pat. No. 3,974,834 to Kane et al discloses an endocardial, bipolar,screw-in lead. With such leads, the physician tactually determines thenumber of rotations necessary to achieve lead fixation.

U.S. Pat. No. 4,046,151 to Rose discloses an endocardial, bipolar,screw-in lead. With such leads, the physician tactually determines thenumber of rotations necessary to achieve lead fixation.

U.S. Pat. No. 4,572,605 to Hess, discloses a typical connector assemblyfor a bipolar coaxial lead. With such leads, the physician tactuallydetermines the number of rotations necessary to achieve lead fixation.

The use of fluoroscopy to detect longitudinal motion is well known incatheter art. See, U.S. Pat. No. 4,771,777 to Horzewski et al. at col.4, Ins. 17-20.

SUMMARY OF THE INVENTION

The present invention aids physicians in determining the amount oftorque to apply when implanting or explanting leads. The number ofrotations applied at the proximal end of the lead is not always equal tothe number of rotations transferred to the distal end of the lead. Thepresent invention provides a radiopaque marker on or near the outerdiameter of the TR (Tip-to-Ring) spacer. The radiopaque marker may beexternal to the lead body or internal to the lead body. It is useful intwo aspects. First, during implant, rotations of the radiopaque torqueindicator strip are easier to count than the rotations of a symmetricalradiopaque helix. Second, after the helix is imbedded in the hearttissue the torque indicator initially appears co-linear; furtherrotation then causes distortion of the radiopaque torque indicator stripinto a spiral configuration. Distortion of the torque indicator isvisible under fluoroscopy as the torque indicator no longer is co-linearto the conductor spring coil and will be visible from all views.

The above features and advantages of the present invention, as well asothers, are accomplished by providing a body-implantable lead having aproximal end and a distal end, the proximal end connected to a medicaldevice, a tissue securing means having a distal end and a proximal end,the tissue securing means extending from the lead body distal end, anelectrical conductor extending between the proximal and distal ends ofthe lead, and a longitudinally extending radiopaque marker affixed tothe lead body proximal to the tissue securing means, the radiopaquemarker showing rotational movement or distortion of the radiopaquemarker under fluoroscopy. The tissue securing means comprises a helixaxially aligned with the lead body and is attached to the electricalconductor. The helix may also be electrically insulated from theelectrical conductor with the lead body having an electrode electricallyconnected to the distal end of the conductor. The radiopaque markercomprises a linear member and consists of a flexible radiopaque materialof a cylindrical shape approximately 0.025 inches (0.0635 cm) indiameter and approximately 0.75 inches (1.9 cm) in length.

Other features, advantages and objects of the present invention willhereinafter become more fully apparent from the following description ofthe drawings, which illustrate the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the lead of FIG. 2 being lodged in and permanently securedto the tissue forming the apex of the right ventricle of the heart;

FIG. 2 shows a view of a body-implantable, endocardial fixed screw leadwith an electrically inactive helix, a separate electrically activeelectrode and an external torque indicator;

FIG. 2a shows a view of the cross-section of FIG. 2 along the lines2--2;

FIG. 3 shows a view of an internal torque indicator inside elevationpartly in longitudinal section which is an alternative embodiment of thedistal end portion of the lead of FIG. 2; and

FIG. 3a shows a view of the cross-section of FIG. 3 along the lines3--3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following specification will first briefly describe the procedurefor implanting a lead then describe the major lead components. Thesecomponents are the electrode, spring coil conductor, torque indicatorand its typical methods of manufacturing, tissue securing means such asthe helix, outer tubing, tip to ring spacer, anode ring and sealingrings. For purposes of this application, the invention will be describedfor use as an endocardial pacing and sensing lead for connecting anartificial cardiac pacemaker to cardiac tissue. Nevertheless, the leadcould as well be applied to other types of body stimulating systems.Although applicant's invention represents an endocardial type lead, theinvention may apply to myocardial leads in the future, as for examplewith endoscopic equipment.

Referring to FIG. 1, the heart 200 in cross section comprises the fourchambers, namely, the right ventricle 205, the right atrium 210, theleft atrium 215 and the left ventricle 220. In the placement of anendocardial lead 110, it is preferable to use a venous approach on thelow pressure side of the heart. For example, the typical ventricularpath as depicted in FIG. 1, would begin through a vein such as the rightor left external subclavian vein, or the right or left cephalic veins,then through the superior vena cava 225, the right atrium 210, thetricuspid valve 230 and to the right ventricle 205. Most screw-in leadsare implanted in the right atrium. The stylet 25 as in FIG. 2 is used tocontrol the location of implant.

After the lead 110 in FIG. 1 is passed through the tricuspid valve 230and into the right ventricle 205, a suitable location for implant may bedetermined by placing the electrode 145 tip adjacent to the heart tissueand taking stimulation and/or sensing thresholds. After a suitablelocation has been determined, the lead 110 is rotated around stylet 25as in FIG. 2 to screw helix 140 into the tissue at the desiredstimulation site. The torque indicator 135 aids the physician indetermining the proper number of rotations. After the helix 140 has beenfirmly affixed to the tissue, the stylet 25 is pulled proximally andremoved from the lead 110.

The present invention can use either a unipolar or a bipolar lead; FIGS.1-3 represent bipolar leads. A bipolar configuration carries twoelectrodes and two conductors. In FIG. 2 which depicts a lead with anexternal torque indicator 35, the two electrodes are shown as the anodering 50 and the electrode 45. FIG. 3 depicts an alternative embodimentof FIG. 2, with FIG. 3 having an internal torque indicator 335. In FIG.3, the two electrodes are shown as the anode ring 350 and the helixelectrode 330. In both the FIG. 2 and FIG. 3 embodiments the twoconductors comprise an outer spring coil and an inner spring coil. Asfor example, in FIG. 3, the outer spring coil is wound about and alongthe axis of the inner spring coil 315. The Tip-to-Ring (TR) Spacer 355provides the electrically insulated separation between the twoelectrodes to permit signal sensing.

In a bipolar lead the two conductors may be co-axial or biaxial coils.In the illustrated embodiments, the coils are co-axial. The conductorspring coil construction is the same in both the external radiopaquemarker 35 embodiment seen in FIG. 2 as in the internal radiopaque marker335 embodiment seen in FIG. 3. The inner and outer conductors are bothspring coils and can be formed of a nickel alloy. The inner spring coil315 distal end is connected to the helix electrode 330 as in FIG. 3 andto the electrode 45 in FIG. 2 by a variety of means, as for example,through the use of a platinum alloy crimp tube. At the proximal end ofboth embodiments the inner spring coil is connected to the pin 60. Theouter spring coil distal end is connected to the anode ring 50. At theproximal end the outer spring coil is connected to the connector ring70. The inner spring coil in both embodiments extends through the lengthof the lead body in a tubular insulating sheath 65 extending between theinner spring coil 15 and outer spring coil, the sheath 65 comprising alumen as seen in FIG. 2A. The outer spring coil extends through thelength of the lead 10 in a lumen of outer tubing 20 of electricallyinsulating material. Both inner spring coil 15 and 315 as well as outerspring coil are formed of electrically conductive material offering lowelectrical resistance and resistance to corrosion by body fluids. Anickel alloy, such as MP35N, is an example of a suitable conductormaterial.

A lead such as 10 using a conductor coil such as inner spring coil 15has been shown to be capable of withstanding constant, rapidly repeatedflexing over a period of time which can be measured in years. The innerspring coil 15 is wound relatively tightly, although there can be aslight space between adjacent turns. The spirally coiled springconstruction of the spring coil 15 also permits a substantial degree ofelongation, within the elastic limits of the material, as well asdistribution of flexing stresses along the conductor which otherwisemight be concentrated at a particular point. Both the inner spring coil15 and the outer tubing 20 are elastic, and this, together with thecoiled construction of the inner spring coil 15, assures maximumdistribution of flexing stresses. The spring coil 15 may also comprise amulti-filar redundant coil of thinner wire.

There are three methods for manufacturing a radiopaque marker for atorque indicator. The most preferable method as seen in FIG. 3 consistsof a two step molding process. The first step molds the platinum loadedsilicone torque indicator into a cylindrical shape. The torque indicatoris removed from the mold after it cures. The second step places thepre-molded indicator into a TR spacer mold in a linear directionpreferably near the outside diameter at a uniform depth and encases thetorque indicator with silicone. A central cavity 375 in the TR Spacermold will form a lumen through which the inner spring coil 315 willextend. The cavity is preferably not symmetrical as a thickened siliconearea should be formed under the torque indicator 335 for strengthening.The cavity 375 contributes to the flexibility of the distal end of thelead body 310. The greater the cavity 375, the greater the flexibility.

The second method of manufacturing torque indicators includesbackfilling a lumen with platinum loaded adhesive as seen in FIG. 3.Mold a second lumen in the TR spacer 355 in addition to the lumen forthe conductor coil. Fill the second lumen which is near the outsidediameter of the TR spacer 355 with uncured platinum loaded adhesive.

The third method of manufacturing a torque indicator, which can be seenin FIG. 2, includes applying an uncured platinum loaded adhesivedirectly to the outside of the TR spacer 55. The adhesive bonds to theexterior of the TR spacer.

Those skilled in the art will recognize that there are other methods ofmanufacturing a radiopaque marker. Radiopaque foils, radiopaque coils orsilicone elastomer with platinum milled in could be used.

The torque indicator 35 or 335 can be made of biocompatible radiopaquematerials such as platinum, iridium, gold or tantalum. It is morepreferably made of platinum loaded silicone with a concentration of 4grams per cc of silicone adhesive. The optional concentration of theradiopaque element is a function of the torque indicator's thickness andtype of radiopaque material selected. The preferred torque indicatordiameter is approximately 0.025 inches (0.0635 cm) with a length ofapproximately 0.75 inches (1.9 cm).

The tissue securing means and electrode could be combined as a unitaryentity or could be separate entities. An example of a unitary entity isa fixed screw lead with the screw as the electrically active electrode330 as in FIG. 3. An example of separate entities is a tissue securingmeans consisting of an electrically inactive fixed helix 40 and aseparate electrically active electrode 45 as in FIGS. 1 and 2.

The tissue securing means can take the form of a relatively rigidcircular corkscrew which can be either an electrically inactive helix 40as in FIG. 2 or helix electrode 330 as shown in FIG. 3. This form of ahelix consists of approximately two closely wound turns ofplatinum-iridium coil made of approximately 0.012 inch (0.0305 cm)diameter wire. These turns end in a sharpened tip 80 or 380 at a pointon the inside circumference on the wire making it up. The tip readilypenetrates the endocardium. The tip further penetrates the tissue withthe addition of clockwise rotation of the proximal lead body. The tipextends beyond the distal end of the lead body by about 0.08 inches(0.20 cm).

When the helix 140 and 40 is electrically inactive as in FIG. 1 and 2respectively, the distal end of the lead additionally has an electrode145 or 45, electrically and mechanically coupled to an inner spring coilby a platinum alloy crimp tube. A flexible, insulating sheath 65surrounds the inner spring coil and crimp tube. A suitable material forthe insulating sheath 65 is silicone rubber. When the helix 40 iselectrically inactive, it serves only as a means of securing andmaintaining the electrode in firm engagement with the endocardialtissue. The helix then forms no part of the electrode structure. Thehelix 140 or 40 can be affixed as follows. The helix may be molded inplace with silicone elastomer. A crimp or laser weld is provided at thedistal end to attach the electrode to the inner spring coil.

To create an electrically active helix electrode 330 as in FIG. 3, thecrimp or laser weld would connect the helix electrode 330 to the innerspring coil 315. The electrically inactive helix 40 and helix electrode330 can both be made of a biocompatible metal, such as platinum, MP35Nalloy, or elgiloy.

Outer tubing 20 or 320 is formed of an electrically insulating material,and preferably a silicone rubber, such as clean room grade Silasticavailable from Dow Corning Corporation or a polyether urethane, such asPellethane ® CPR ® 2363-80AE available from the Upjohn Company. Thesematerials are additionally suitable because they are inert and welltolerated by body tissue. In any of the disclosed embodiments the distalend of the lead body should be more flexible than the proximal end ofthe lead body to prevent undue stress on the myocardium. This regionwill generally be more flexible because only the inner spring coil 15 or315 is present, the outer spring coil having ended at the anode ring 50or 350. Further flexibility can be accomplished by either decreasing thethickness of the TR spacer 55 or 355 wall or using more flexiblematerial at the distal end of the outer tubing 20 or 320 than at theproximal end of the outer tubing. Furthermore, in the FIG. 3 internaltorque indicator embodiment, the size of cavity 375 can be adjusted. Thegreater the cavity 375, the greater the flexibility.

The TR (Tip to Ring) spacer 55 lies between the anode ring 50 and thehelix 40 in FIG. 2 or between the anode ring 350 and the helix electrode330 in FIG. 3. It is made of insulating material such as silicone. Itelectrically insulates the inner spring coil 15 or 315 from the tissue.

The anode ring 50 or 350 is electrically active and completes theelectrical circuit. It is typically formed of a polished platinum alloywith an exposed surface area much larger than that of the electrode 45in FIG. 2 or helix electrode 330 in FIG. 3.

Sealing rings 95 and 90 as in FIG. 2 both serve to prevent entry of bodyfluids into the lead assembly and prevent electrically shorting by aconductive fluid. They also mechanically stabilize the lead within thepacemaker connector block. The proximal end of the lead body is the samefor both the FIG. 2 external torque indicator embodiment as for the FIG.3 internal torque indicator embodiment. Sealing rings can be affixedwith a variety of methods, one of which follows. The first sealing ring95 lies over the top of a crimp tube to which the inner spring coil 15or 315 is connected. The inner spring coil is also connected to the pin60. The first sealing ring 95 prevents shorting by a conductive fluidpath from the pin 60 to the connector ring 70. The second sealing ring90 lies over the top of a crimp tube to which the outer spring coil isconnected. The second sealing ring prevents shorting by preventing afluid path between the body tissue and the connector ring 70.

The preceding specific embodiments are illustrative of the practice ofthe invention. It is to be understood, however, that other expedientsknown to those skilled in the art or disclosed herein, may be employedwithout departing from the spirit of the invention or the scope of theappended claims.

    ______________________________________                                        No.            Component                                                      ______________________________________                                         10            Lead                                                            15            Inner Spring Coil                                               20            Outer Tubing                                                    25            Stylet                                                          35            External Torque Indicator                                       40            Electrically Inactive Helix                                     45            Electrode                                                       50            Anode Ring                                                      55            TR Spacer                                                       60            Pin                                                             65            Insulating Sheath                                               70            Connector Ring                                                  80            Tip                                                             90            Second Sealing Ring                                             95            First Sealing Ring                                             110            Lead                                                           135            External Torque Indicator                                      140            Electrically Inactive Helix                                    145            Electrode                                                      180            Tip                                                            200            Heart                                                          205            Right Ventricle                                                210            Right Atrium                                                   215            Left Atrium                                                    220            Left Ventricle                                                 230            Tricuspid Valve                                                310            Lead                                                           315            Inner Spring Coil                                              320            Outer Tubing                                                   330            Helix Electrode                                                335            Internal Torque Indicator                                      350            Anode Ring                                                     355            TR Spacer                                                      375            Cavity                                                         380            Tip                                                            385            Crimp Tube                                                     ______________________________________                                    

What is claimed is:
 1. A body-implantable lead comprising:a lead bodyhaving a center axis, a proximal end and a distal end; means forsecuring said distal end of said lead body to tissue, said means forsecuring extending from said lead body distal end; an electricalconductor extending between said proximal and distal ends of said leadbody; and a radiopaque marker having a center axis, said radiopaquemarker affixed to said lead body at a position so that said radiopaquemarker center axis is offset from said lead body center axis whereinsaid lead body has a first section and a second section, said firstsection has greater flexibility than said second section, and saidradiopaque marker is affixed to said first section of said lead body. 2.A lead according to claim 1 wherein said radiopaque marker is affixed tosaid lead body proximal to said means for securing said distal end ofsaid lead body to tissue.
 3. A lead according to claim 1 wherein saidmeans for securing said distal end of said lead body to tissue comprisesa helix axially aligned with said lead body.
 4. A lead according toclaim 3 wherein said helix is connected to said electrical conductor. 5.A lead according to claim 3 further comprising said helix is at leastpartially insulated.
 6. A lead according to claim 5 having an electrodeelectrically connected to said conductor at said distal end of said leadbody.
 7. A lead according to claim 1 wherein said radiopaque markercenter axis is parallel to said lead body center axis.
 8. A leadaccording to claim 1 wherein said first section has a cavity.
 9. A leadaccording to claim 8 wherein said radiopaque marker comprises a linearmember.
 10. A lead according to claim 9 wherein said radiopaque markeris flexible.
 11. A lead according to claim 9 wherein said radiopaquemarker has a linear cylindrical shape.
 12. A lead according to claim 1wherein said radiopaque marker is affixed internally to said lead body.13. A lead according to claim 12 wherein said conductor and saidradiopaque marker are separated by a cavity.
 14. A lead according toclaim 1 wherein said radiopaque marker is affixed externally to saidlead body.
 15. A body-implantable lead comprising:a lead body having anouter wall, a proximal end and a distal end; an electrical conductorextending between said proximal and distal ends of said lead body; ahelix attached to said distal end of said lead body, said helix axiallyaligned with said lead body; and a radiopaque marker affixed to saidouter wall of said lead body proximal to said helix Wherein said leadbody has a first section and a second section, said first section beinglocated near said distal end, said second section being located nearsaid proximal end, said first section be in a more flexible than saidsecond section.
 16. A body-implantable lead according to claim 15wherein said helix is electrically attached to said conductor.
 17. Abody-implantable lead according to claim 15 further comprising anelectrode positioned at said distal end of said lead body said electrodeconnected to said conductor.
 18. A body-implantable lead according toclaim 15 wherein said first section has a non-symmetrical cavity.
 19. Abody-implantable lead according to claim 15 wherein said first sectionhas a cavity.
 20. (New) A body-implantable lead according to claim 15wherein said radiopaque marker is integral with said lead body.